Determination of Stoichiometric Dissociation Constants of Formic Acid in Aqueous Sodium or Potassium Chloride Solutions at 298.15 K

Abstract

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant K m of formic acid in dilute aqueous NaCl and KCl solutions at 298.15 K from the thermodynamic dissociation constant K a of this acid and from the ionic strength I m of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study, and the equations for K m were based on the single-ion activity coefficient equations of the Hü ckel type. The data measured by potentiometric titrations in a glass electrode cell were used in the estimation of the parameters for the Hü ckel equations of formate ions. The Hü ckel parameters obtained in these estimations agree well with those published previously for acetate ions, and therefore, the acetate parameters are also recommended for formate ions. By means of the calculation method based on the Hü ckel equations, K m can be obtained almost within experimental error at least up to I m of about 2 mol kg -1 for formic acid in NaCl and KCl solutions.

Determination of the second stoichiometric dissociation constants of glycine in aqueous sodium or potassium chloride solutions at 298.15 K

“…From the results of these formic acid titrations, the K m values were determined by the method suggested in ref. 10. This method is principally the same as the one used here for glycine.…”

“…The K m values obtained from the titrations were always very close to those calculated from the equations recommended in ref. 10 for K m of formic acid in NaCl or KCl solutions. The good agreement between the observed and recommended K m values for this acid guarantees the quality of the new data for glycine.…”

“…In this manuscript, we continue the studies (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) dealing with the thermodynamics of weak acid solutions. The purpose of these studies is to determine the stoichiometric dissociation constants (for example, the molality scale dissociation constants, K m ) for salt solutions of different weak acids, as reliably as possible from potentiometric titration data measured with glass electrodes.…”

Determination of Stoichiometric Dissociation Constants of Glycolic Acid in Dilute Aqueous Sodium or Potassium Chloride Solutions at 298.15 K

“…In this study, we continue the studies [1][2][3][4][5][6][7][8][9][10][11] dealing with the thermodynamics of weak acid solutions. The purpose of these studies is to determine the stoichiometric dissociation constants (for example the molality scale dissociation constants, K m ) for solutions of different weak acids as reliably as possible from potentiometric titration data and, additionally, from literature data obtained by galvanic cells without liquid junctions.…”

“…The most reliable values in these tables have been determined by either the conductometric method or by the method based on electromotive force (emf ) data measured on Harned cells. Thus, glycolic acid is somewhat weaker than the strongest unsubstituted aliphatic carboxylic acid, formic acid, for which K a = 1.82 · 10 −4 [10,14]. Thus, glycolic acid is somewhat weaker than the strongest unsubstituted aliphatic carboxylic acid, formic acid, for which K a = 1.82 · 10 −4 [10,14].…”